: A large diaphragm is usually inside the saucer-shaped vessels (look at commercial-sized gas regulators outside of large buildings like motels and malls.)

: Old solid-fuel boilers often had arms that operated off the diaphragm that had the air-shutter damper to the fire chamber; they might be lost over time. As the pressure rose in the system, the damper closed to reduce fire, keeping a steady burn.

I have a presure relief on the boiler water supply line between the boiler and the solenoid supply valve. Where can I go to find out what meets code?